Computer input and other pointing devices, such as electronic mice, convert physical movement into movement of a cursor or other image across a computer screen. Previously, many such devices utilized mechanically driven encoder wheels and other moving components to detect direction and magnitude of motion, and to then convert that information into data for communication to a computer or other device. Optical surface tracking offers an improved method of motion detection. Instead of encoder wheels rotated by a ball rolling across a surface, an array of photo-sensitive elements generates an image of a desktop (or other supporting surface) portion when light from an associated illumination source (such as a light emitting diode) reflects from the desktop or other surface. Subsequent images are compared, and based on the correlation between images, the magnitude and direction of mouse motion may be determined. Exemplary optical tracking systems, and associated signal processing techniques, include those disclosed in commonly owned U.S. Pat. Nos. 6,172,354, 6,303,924 and 6,373,047.
An optically-tracking computer mouse typically includes an outer housing that is configured to be grasped by the user and moved across a supporting surface such as a desk top or a table. A region on a bottom portion of the housing is either transparent or open so that light may reach a portion of the supporting surface (or “target area”) and be reflected back into the housing. A light source inside of the mouse, which is typically a LED, is selectively turned on and off so as to controllably illuminate the target area. Light from the LED reflects from the target area and is collected and focused by a lens (inside the mouse housing) through an aperture and onto a photosensing surface of an image sensor (also inside the housing). The image sensor then forms (sometimes in connection with other components) an image of the target area. Typically, the image sensor is attached to a printed circuit board (PCB).
Existing optically-tracking devices direct light to a target area in various manners. In some cases, the LED is positioned between the image sensor and the target surface. Although simple in some respects, this configuration can add additional steps to an assembly process, and can also be a potential source of errors because of improper alignment. Moreover, many commercially available LEDs are not optimized for direct illumination of a near-field object (such as a target area of a tracking surface), resulting in less-than-desirable illumination patterns. Other configurations use a light guide to direct light from a LED to the target area. Typically, a light guide is formed from light-transmissive material such as glass or plastic, and is positioned between the LED and the target area. Light from the LED enters the light guide at one end, reflects from one or more internal surfaces of the light guide, and then exits from another end of the light guide to illuminate the target area.
In another line of development, computer input devices have been configured to illuminate an external portion of the device that is visible to the user. This externally visible light addresses various issues. For example, a conventional mouse may be difficult to locate in low light conditions, potentially making mouse (and computer) use less efficient. More particularly, in order to enhance the visibility of the information displayed on a computer screen and to reduce glare from the screen, computers are often operated in either low or no light conditions. Operations requiring the use of the mouse are typically performed periodically, requiring the user to frequently move his or her hand from the keyboard to the mouse. Although the mouse is usually within reach of the user, it may be difficult to locate and orient the mouse if the user cannot easily see it. By the making mouse more visible, the user may spend less time fumbling for the mouse.
An externally visible light also provides other advantages. For example, such a light can be used as an indicator that the computer is still turned ON. In many cases, a housing containing the computer central processing unit (CPU) and other components may be located under a desk or table, or otherwise hidden from view. An ON/OFF indicator light located on the CPU housing might thus be difficult to see. If the computer has a screen saver feature, the user might not realize the computer is turned ON. A mouse, however, is normally placed in a more visible location. Even if a screen is blank and the CPU housing hidden from view, the user can easily determine if the computer is ON or OFF by glancing at the mouse. Further details of a computer input device with an externally visible light can be found in, e.g., commonly owned U.S. Pat. No. 6,486,873.
In existing configurations of optically tracking input devices with an externally visible light, one LED (or other light source) illuminates the target area and another LED (or other source) provides the externally visible light. This configuration presents several disadvantages. Two LEDs draw significant power and can reduce battery life in wireless or other battery operated components (e.g., a wired mouse connected to a battery powered laptop computer). Often, a separate PCB is necessary to hold the externally-visible LED. This increases assembly steps and manufacturing costs, as does the need to buy two LEDs for each device.